This invention pertains to a cone-shaped screen for attachment to the end of a culvert pipe for preventing beavers from constructing a dam upon the end of, or inside the culvert pipe. More particularly, the present invention pertains to a double layered cone-shaped screen with aperture dimensions selected to refuse access to beavers and to let local fish and floating debris there through.
A culvert pipe along a stream represents an ideal flow restriction upon which a beaver can build a dam. In periods of rising water due to heavy rains or melting snow for example, such dams are known to cause road flooding and road undermining which often result in extensive damage. Road maintenance personnel usually try to dismantle a beaver dam at an early stage of its construction. As part of the dismantling process, the beavers are trapped and re-located in deeper forests. This relocation of the animals is a temporary solution because other beavers usually come along and start all over. Therefore it is preferable to install permanent screens over the ends of a culvert pipe in which flows an active brook or stream, to discourage any beaver from attempting to construct a dam at that location.
Certain types of screens or grates mounted over the end of a culvert pipe are known to be efficient devices for discouraging beavers from building a darn. However, such screens or grate must be made so that the flow of water through the culvert pipe, in all seasons, is not adversely affected. Similarly, the circulation of the local fish through the screen must be maintained such that the natural fish habitat is not disturbed. It is believed that these two particular requirements for an efficient beaver control screen represent some challenges and have not been properly addressed in the past.
It is known that several types of beaver control screens and grates have been developed and used in the past with varying degrees of success. Some of these inventions are described herein below.
The first type of culvert pipe screen of the prior art consists of a wire strainer mounted inside the pipe, to prevent rodents from entering the pipe and freely circulating inside the pipe. Culvert pipe screens of this type are described in the following patents:
U.S. Pat. No. 906,562, issued on Dec. 15, :1908 to C. S. Rue et al.;
U.S. Pat. 5,090,152, issued on Feb. 25, 1992 to R. Ling.
A second type of screen consists of a grating mounted over the end of a culvert pipe. The grating has a flat surface and is made of parallel and perpendicular bars affixed to each other and to the pipe. Some of these screens are described in the following patents:
U.S. Pat. No. 3,587,239, issued on Jun. 28, 1971 to O. A. Feland;
U.S. Pat. No. 5,037,542, issued on Aug. 6, 1991 to K. T. Carroll;
U.S. Pat. No. 4,713,179, issued on Dec. 15, 1987 to S. J. Goedderz, Sr.;
CA Pat. No. 1,234,766, issued on Apr. 5, 1988 to E. B. Piercy et al.
The prior art also contains a cylindrical screen made of wire mesh and which completely encloses the upstream end of a culvert pipe. An example of this type of culvert pipe screen is described in:
CA Pat. No. 1,290,578, issued on Oct. 15, 1991 to N. J. Thurber.
Although several solutions have been proposed to the problems caused by beavers near culverts, it is believed that the prior art systems and devices are deficient in at least several important features. For example, some of the bars or rods of the screen are perpendicular to the flow of water and promote the accumulation of floating debris against the surface of the screen. A clogged screen on the end of a culvert pipe has a similar effect as a beaver dam, as the water accumulating at that location could also cause road flooding and road undermining. Also, a flat screen mounted over the end of a culvert pipe, or inside the pipe, does not prevent a beaver from anchoring a dam on the end of the culvert pipe. Therefore, flat screens are not considered to be an efficient solution to control beaver problems.
The deficiencies of flat screens have prompted other inventors to develop cone-shaped screens which extend away from the end of the culvert pipe and which are more efficient in preventing access to the end of the culvert pipe to a beaver. The cone-shaped screen normally makes an acute angle with the water currents and is therefore less susceptible to clogging. A cone-shaped screen also has a large surface as compared to the cross-section area of the culvert pipe on which it is mounted, and therefore more debris is required to clog it.
Therefore, the type of beaver control screen which is of interest herein has a conical shape and is secured to either end of a culvert pipe. Some examples of conical screens of the prior art are described in the following documents:
U.S. Pat. No. 2,970,697, issued on Feb. 7, 1961 to E. L. Larson et al.;
U.S. Pat. No. 3,472,030, issued on Oct. 14, 1969 to R. E. Rieke;
U.S. Pat. No. 5,102,537, issued on Apr. 7, 1992 to J. R. Jones;
CA Pat. No. 208,647, issued on Feb. 22, 1921 to L. H. Bradburn.
However, a conical screen has rods or bars which converge toward the apex thereof. When the cone-shaped screen is installed on the downstream end of a culvert pipe, these converging rods, with the force of water, act as a trap where fish can become caught. Therefore, the converging rods of cone-shaped screens are not recommended as they could eventually destroy the local fish population.
As such, it may be appreciated that there continues to be a need for a new and improved beaver control screen for installation on culvert pipes, which can be efficiently used to discourage the construction of beaver dams, which does not clog easily and which does not hinder the migration of local fish there through.
The beaver control screen according to the present invention has three main purposes. Firstly, the beaver control screen is made to protect the entire culvert against damages caused by debris transported by water, especially,during spring thaw periods and during heavy rainstorms. Secondly, the present invention is made to efficiently prevent beavers from building a dam on the end of a culvert pipe or inside a culvert pipe. Thirdly, the beaver control screen is made to preserve the natural fish habitat.
In accordance with a first aspect of the present invention, there is provided a beaver control screen comprising a cone-shaped screen having a base, an apex and a central horizontal axis and a length between the base and the apex. The cone-shaped screen has a first set of spaced-apart straight rods extending from the base to the apex and being disposed in a first conical layer. A second set of spaced-apart straight rods is disposed in a second conical layer inside the first conical layer and extends toward the apex over a distance of about one-half the length of the first conical layer. The second conical layer is disposed in a concentric relationship with the first conical layer. Each rod in the first conical layer is spaced away from an adjacent rod in the second conical layer a same spacing of about 3 inches along this adjacent rod. This spacing has been found to be advantageous for preventing access to the culvert pipe to adult and juvenile beavers, and on the other hand, has been found to be relatively tolerant to the passage of floating debris through the screen.
A beaver dam is usually built using intertwined branches and twigs of various sizes, cemented with mud, lichen and other aquatic plants. The smooth surface of the rods and the spacing between the rods at the base of the beaver control screen according to the present invention prevent the beavers from building a foundation of branches and twigs across the opening of the culvert pipe.
According to another feature of the present invention, the apex of the cone-shaped screen is made with an annular plate having an outside edge and an inside edge. The rods in the first conical layer are alternately affixed to the outside edge and to the inside edge. In this arrangement, a minimum spacing between any two adjacent rods in the screen can be made to be larger than other prior art arrangements where all the rods are affixed to each other or to the outside edge of the apex plate for examples. In areas where local fish species such as the char, (Salvelinus), co-habit with beavers, the minimum spacing between the rods is made to be at least about 1.25 inches, such that the converging rods of the screen do not constitute traps which could threaten the survival of fish population.
In accordance with yet another feature of the present invention, the beaver control screen is affixed to the culvert pipe by means of a hinge on the upper segment of culvert pipe. The hinge has a horizontal articulation axis. The beaver control screen according to the present invention is simply tilted upward about the hinge to clear any debris that might accumulate on its surface.
Other advantages and novel features of the present invention will become apparent from the following detailed description.